Corrosion of metallic components in industrial plants may cause system failures and sometimes plant shutdowns. In addition, corrosion products accumulated on the metal surface will decrease the rate of heat transfer between the metal surface and the water or other fluid media, and therefore corrosion will reduce the efficiency of the system operation. Thus, corrosion can increase maintenance and production costs and decrease the life expectancy of the metallic components.
The most common way to combat corrosion is to add corrosion inhibiting additives to the fluid of such systems. However, currently available corrosion inhibiting additives are either non-biodegradable, toxic, or both, which limits the applicability of such additives.
Regulatory pressures have been steadily increasing to eliminate discharge of molybdate and/or nitrite to the environment. Furthermore, nitrite treatments can develop serious microbiological growth in the closed loop. In actuality, the most reliable treatments to eliminate corrosion in closed loop systems are based on molybdate, nitrite or a combination of the two. Existing all-organic treatments do not perform well in systems where corrosion has occurred, and iron and/or iron oxide levels are high, or the water in the closed system has aggressive ions. The water composition as found in closed loops can vary significantly.
Thus, environmental concerns are driving the use of corrosion inhibitors away from heavy metals, molybdenum and nitrite. Existing purely organic treatments, although desirable, are not reliable when applied in iron or iron oxide laden systems or aggressive waters. By their nature, closed loops are prone to have high iron.
Therefore, there is a strong need for an environmentally friendly, non-molybdenum, non-nitrite corrosion inhibitor treatment for closed loop systems. In the present invention, a combination of an organic acid, a triamine and a phosphonate compound surprisingly provides enhanced protection of metallic surfaces from corrosion in closed loop systems. The organic treatments of the present invention can provide good corrosion protection in aggressive water either with or without hardness, and even in corroded systems.